THE GYMNOCHROMES - NOVEL MARINE BROMINATED PHENANTHROPERYLENEQUINONE PIGMENTS FROM THE STALKED CRINOID GYMNOCRINUS-RICHERI

Five novel brominated phenanthroperylenequinone pigments, gymnochromes A-D (1-4) and isogymnochrome D (5), were isolated from the stalked crinoid Gymnocrinus richeri. The structures of the compounds were inferred from their spectra (IR, UV-vis, H-1 and C-13 NMR, FABMS). The presence of both bulky hydroxy groups at positions 10 and 11 and side chains at positions 3 and 4 causes sufficient crowding to force the octacyclic phenanthroperylenequinone system into a nonplanar helical shape. This helicity generates axial chirality in the molecules. The presence of chiral carbon atoms in the side chains gives rise to diastereomers. The absolute configurations of the chiral carbons and the axial chirality of the natural pigments was inferred from CD and NMR data and by correlations made with cercosporin and other naturally occurring perylenequinones. The configurations assigned to the chiral carbons in the side chains of compounds 4 and 5 were confirmed by the results of the application of Horeau's method of kinetic resolution.